Piston alloy



E. MAHLE Dec. 19, 1933.

PISTON ALLOY Filed Oct. 3Q, 1931 IN V EN TOR.

MINI] BY W ATTORNEYS.

Patented Dec. 19, 1933 PISTON Ernst Mable, Stuttgart,

Elektronmetall G. m. gart, Germany ALLOY Germany, assignor to b. 11.,Cannstatt-Stutt- Application October 30, 1931, Serial No. 572,071, andin Germany November 1, 1930 6 Claims.

During recent years, light metal alloys have come more and more intofavour as piston materials, in place of the grey cast iron at one timeexclusively used for that purpose. It has,

however, been found that the low hardness of these light-metal alloys athigh temperatures constitutes a defect which must be set off against thenumerous favourable properties which have substantially contributed tothe extended use of said alloys. serious in the This defect becomesextremely piston-ring grooves, inasmuch as the grooves which are exposedto the greatest thermal action, namely near the head, are unable toofier any prolonged resistance to the impact of the piston rings, butbecome battered at the prevalent high temperatures, so that the pistonsare no longer accurately guided, and, in some events, are even rendereduseless. Attempts to improve the high-temperature hardness of the lightmetals to a substantial extent by incorporating new alloying components,have failed,

It has now been ascertained in accordance with the invention,

that certain beryllium bronzes, which must be classed among the heavymetals, exhibit a quite unusual high-temperature r hardness which seemsto render them particularly suitable as structural material for pistons,

at least for the ring portions of same, In such case the actual bodymade of light metal,

of the piston can still be that portionoi the end,

in which the piston rings are fitted, being rolledin or integrallycast-in an annular shell. However, the entire end of the piston,including the portion carrying the piston rings,

may also consist of beryllium bronze.

As compared with the suggestions for improving the high-temperaturehardness of the ring portion by constructing it of grey cast iron andsuitably connecting it with the other, lightmetal, portion of thepiston, the" construction of the ring portion of beryllium bronze, inaccordance with the invention, offers the advantage that the thermalexpansion of these alloys approximates far more closely. to that of thelight-metal alloys, so

' disadvantages arising that many constructional from the necessity ofob- .sion of the beryllium bronzes,

taining secure connection between the cast iron and light-metal parts ofthe piston are obviated.

A further advantage over that arrangement consists also in that the heatconductivity of the copper-beryllium alloys is superior to that of greycast iron, so that the good conductivity constituting one of the mainadvantages of the light-metal alloys is not impaired, in the presentcase, to the same extent as when cast iron is used for the ring portion.

In view of the relatively high thermal expanit is advisable, wherestress is laid on the noiseless running of the engine, to employcopper-beryllium alloys solely for that portion of the piston thatcarries the rings, and to make the skirt for which hightemperaturehardness and heat conductivity are of minor importance, of grey castiron or steel plate. In this manner a method or construction is attainedin which a head of light metal is surrounded by a beryllium-bronzeshell, provided with the piston-ring grooves and carrying a skirtportion of iron, the several structural components being connectedtogether in known manner, but without the previously encountered diffi-0 culties, since the difierences in the coefficients of thermalexpansion of the successive materials merge gradually into one another.

In order more clearly to understand the invention, reference is made tothe accompanying drawing which illustrates by way of example, twoembodiments of pistons constructed in accordance therewith and in which:

Fig. 1 is a vertical section taken through the gudgeon pin bosses, ofone embodiment;

Fig. 2 is a vertical section taken at right angles, to Fig. 1;

Fig. 3 is a plan section along the line A-B of Fig. 1; and

Fig. 4 is a vertical section taken through the gudgeon pin bosses, of asecond embodiment.

In both embodiments the piston head 1 is made of light metal, in orderto reduce the moving mass, whilst a portion 2, carrying the piston ringsand secured shown in Figs. 1 to 3 or by ribs 5, integrally cast with theshell 2 in in Fig. 4. i

In other cases, (such as Diesel engines) where high thermal expansion inthe piston skirt is a matter of no importance, the skirt also mayconsist of beryllium bronze, it being advisable to incorporate a certainamount of manganese in the alloy, in order to increase the resistance toabrasion.

Materials that have been found particularly suitable for the purpose ofthgpresent invention, are binary alloys of copper with up to 5 percent(preferably about 2.5 percent) of beryllium, which still exhibit ahigh-temperature hardness of about 200 Brinell at 350 C. Increasedresistance to abrasion, with the same high-temperature hardness, isobtained by the employment of certain alloys of copper with minorquantities of beryllium and manganese, which may be subjected to heattreatment with a 'view of further improving their hardness at lowertemperatures. Thus, an alloy containing about 1.5 percent of berylliumand about 3 percent of manganese, the balance being copper, has ahardness of about 200 Brinell at 350 C. in the untreated as Well as theheat-treated form. At ordinary temperatures, however, the hardness ofthe untreated alloy amounts to only about 150 Brinell, whereas, after aheat treatment comprising heating the alloy to about 750 C. and thenquenching, the hardness at ordinary temperatures rises up to about 300Brinell.

I claim:

1. A piston for internal combustion engines having a ring-bearingportion composed of a beryllium bronze, having copper as its mainconstituent and containing between about 1 and about 5 percent orberyllium, and having the portion contacting the ring-bearing portioncomposed of a difierent metal having a coefficient of expansionapproximating that of the beryllium bronze.

2. A piston for internal combustion engines having a ring-bearingportion composed of a beryllium bronze, having copper as its mainconstituent and containing between about 1 and about 5 percent ofberyllium, and about 3 perthe embodiment shown cent of manganese, andhaving the portion contacting the ring-bearing portion composed of adiiTerent metal having a coeihcient of expansion approximating that ofthe beryllium bronze.

3. A piston for internal combustion engines having a ring-bearingportion composed of a beryllium bronze, the constituents of which areabout 1 to about 5 percent of beryllium, about 3 percent of manganese,the remainder being copper, and having the portion contacting theringbearing portion composed of a different metal having a coeificientof expansion approximating that of the beryllium bronze.

4. A piston for internal combustion engines having a ring-bearingportion composed of a beryllium bronze, the constituents of which are1.5 percent of beryllium, 3 percent of manganese, and 95.5 percent ofcopper, and having the portion contacting the ring-bearing portioncomposed of a different metal having a coefficient of expansionapproximating that of the beryllium bronze.

5. A piston for internal combustion engines comprising a piston-head oflight metal, an annular shell composed of a beryllium bronze havingcopper as its major constituent and containing between about 1 and about5 percent of beryllium and having a coeflicient of expansionapproximating that of said light metal surrounding said piston head,grooves adapted to receive piston rings in said annular shell and askirt portion substantially consisting of iron connected with saidannular shell.

6. A piston for internal combustion engines comprising a piston head oflight metal, an annular shell, composed of a beryllium bronze, theconstituents of which are between about 1 and about 5 percent ofberyllium, 3 percent of manganese, and the remainder of copper, and thecoemcient of expansion of which approximates that of said light metal,surrounding said piston head, grooves adapted to receive piston rings insaid annular shell and a skirt portion substantially consisting of ironconnected with said annular sh'ell.

- ERNST MAHLE.

